1. Field
The following description relates to a capacitor type humidity sensor. An MIM (Metal-Insulator-Metal) capacitor or a PIP (Polysilicon-Insulator-Polysilicon) capacitor is used as a reference capacitor (CR) to enable trimming.
2. Description of Related Art
A humidity sensor is configured to detect a change in humidity based on an electrical signal, and recently humidity sensors have been embedded in a smart device, such as a smart phone. A humidity sensor recognizes ambient humidity and can be used to visually check the comfort of users.
A humidity sensor optimized for the smart device measures humidity by measuring a change in electrical properties of humidity sensitive materials. The electrical properties include resistance, capacitance, and resonant frequency. A resistive humidity sensor has variable electrical resistance and a capacitor type humidity sensor has variable capacitance according to the humidity.
The capacitor type humidity sensor exhibits long-term reliability and linear property of sensor as compared to the resistive humidity sensor. Thus, the capacitor type humidity sensors are generally chosen for products requiring a high degree of precision and are applicable to a very broad range of products.
The capacitor type humidity sensor is manufactured in capacitor form in which a humidity sensitive polymer such as polyimide, which exhibits variable dielectricity when it absorbs moisture, is used as a dielectric material.
The typical capacitor type humidity sensor consists of a sensing capacitor and a reference capacitor. The capacitance value of sensing capacitor changes in accordance with the humidity and that the capacitance value of reference capacitance is maintained as being constant. A size of the reference capacitor is the same as that of the sensing capacitor in order to remove offsets of sensing capacitor, and the reference capacitor is aligned adjacent to the sensing capacitor.
In the example illustrated in FIG. 1, the size of the sensing capacitor (Cs) 10 and the size of the reference capacitor (Cr) 12 are the same. The sensing capacitor and the reference capacitor are aligned adjacent to each other.
Despite the above-discussed structure and the size of the sensing capacitor (Cs) 10 and the reference capacitor (Cr) 12, there may be offset differences due to process variation and property differences due to moist-permeable material. As a result, the offset is not substantially removed and removing the offset of the sensing capacitor (Cs) is difficult. In other words, humidity cannot be detected accurately and errors occur.